conditioning fused kernels

        data_size = input.size()

        query_seq_len = data_size[-2]

        key_seq_len = data_size[-1]

        attn_batch_size = data_size[0] * data_size[1]

        assert input.dim() == 4

        # invoke custom kernel

        if self.input_in_fp16 and key_seq_len <= 2048 and mask is not None and \

           query_seq_len % 4 == 0 and self.scaled_masked_softmax_fusion:

           query_seq_len % 4 == 0 and key_seq_len > 16 and \

           attn_batch_size % 4 == 0 and self.scaled_masked_softmax_fusion:

            scale = self.scale if self.scale is not None else 1.0